1. Field of the Invention
The present invention relates to a seat reclining apparatus for adjustment of the seatback angle of a reclining seat.
2. Description of Related Art
Japanese Unexamined Patent Publication No. 2012-51466 discloses a known seat reclining apparatus which includes a base plate which is fixed to a seat cushion frame, a ratchet plate (ratchet) which is fixed to a seatback frame and provided on the inner periphery thereof with an annular internal gear, a rotational center shaft (hand-operated shaft) for the base plate and the ratchet plate, a plurality of (three) lock members (pawls) which are supported on an inner side of the base plate (a surface of the base plate which faces the ratchet plate) thereby to be movable (slidable) relative to the base plate in radial directions of the rotational center shaft, a rotational cam which rotates with the rotational center shaft, and a lock spring (spiral spring) which biases and rotates the rotational center shaft.
An outer toothed portion is formed on an outer peripheral surface of each lock member. Each lock member is movable relative to the base plate (the associated guide groove) between an engaged position in which the outer toothed portion is engaged with the internal gear of the ratchet plate and a disengaged position in which the outer toothed portion is disengaged radially inwards from the internal gear of the ratchet plate.
The rotational cam is rotatable between a locked position to position each lock member in the engaged position and an unlocked position to position each lock member in the disengaged position. The lock spring biases the rotational center shaft in a direction to rotate the rotational cam toward the locked position.
Welding protrusions are protruded from an outer side of the base plate (a surface of the base plate which faces the seat cushion frame). The welding protrusions can be engaged in a holding portion which is formed in the seat cushion frame as a through-hole (note that neither the seat cushion frame nor the holding portion is disclosed in Japanese Unexamined Patent Publication No. 2012-51466). The welding protrusions are fixed to the seat cushion frame by welding a weld zone (fixed portion) which is formed on a portion of the peripheral edge of each welding protrusion to a portion of the peripheral edge of the aforementioned holding portion of the seat cushion frame. In addition, a pressure receiving portion which is formed on another portion of the peripheral edge of each welding protrusion comes in contact with another portion of the peripheral edge of the aforementioned holding portion.
When an operating lever (hand-operated lever) which is linked with the rotational center shaft is not manually rotated, the rotational cam rotates toward the locked position by the rotational biasing force of the lock spring, which causes each lock member to move toward the engaged position. Accordingly, the outer toothed portion of each lock member is engaged with the internal gear of the ratchet plate, so that the seatback frame (seatback) becomes nonrotatable relative to the seat cushion frame (seat cushion).
On the other hand, when the operating lever is manually rotated against the rotational biasing force of the lock spring, the rotational cam moves to the unlocked position. Thereupon, each lock member is at (has been moved to) the engaged position moves toward the disengaged position, which causes the outer toothed portion of each lock member to be disengaged from the internal gear of the ratchet plate. As a result, the seatback frame (seatback) becomes rotatable relative to the seat cushion frame (seat cushion) (i.e., the angle of the seatback becomes adjustable relative to the seat cushion).
Additionally, if a collision load occurs between the pressure receiving portions of the welding protrusions and the peripheral edge of the holding portion of the seat cushion frame by a rotation of the seatback frame (seatback) relative to the seat cushion frame (seat cushion) in the seat reclining apparatus in a locked state due to, e.g., a vehicle which incorporates the seat reclining apparatus colliding with another vehicle, the pressure receiving portions of the welding protrusions and the peripheral edge of the holding portion of the seat cushion frame receive this collision load.
In general, the base plate is produced by press-forming a metal plate using a mold having molding depressions (depressed portions) and a mold having molding protrusions (protruded portions). Accordingly, the aforementioned welding protrusions, which are molded in the molding depressions of the former mold thereby, are formed on the outer side of the base plate, while depressions (protrusion-corresponding depressions) which are molded by the molding protrusions of the latter mold (to be recessed toward the welding protrusions) are formed on the inner side of the base plate at positions corresponding to the positions of the welding protrusions. An annular bridging portion is formed at a portion of the base plate which connects the peripheral edge of each welding protrusion and the peripheral edge of the associated protrusion-corresponding depression.
Since the pressure receiving portions of the welding protrusions are for receiving loads such as a collision load as described above, it is desirable that the aforementioned annular bridging portion, which correspond to the pressure receiving portions, be formed to have a large wall thickness (greater than portions of the base plate which correspond to the welding protrusions).
However, in a known base plate, the wall thickness of the aforementioned annular bridging portion and the cross sectional shape of the outer peripheral portion of each welding protrusion are the same at any circumferential position of this welding protrusion, thus not being appropriately shaped according to each circumferential position thereof.